Inducer



9 1964 M. c. HUPPERT ETAL 3,153,119

INDUCER Filed July :5, 1961 26 3:. 2 l 37 OUTLET INLET BLADE 2o LEAD ROTATIONAL T W ms TRACE OF/- BLADE AT RMS a PERPENDICULAR TO HUB AXIS BLADE Q HUB AXIS- FIG. 2

INVENTORS MERLEC. HUPPERT JOHN R. PARKER AGENT United States Patent 3,163,119 INDUCER lllerle C. Huppert and John R. Parker, Woodland Hills, Calih, assignors to North American Aviation, inc. Filed July 3, 1961, Ser. No. 121,425 8 Qlaims. (Cl. 103-89) This invention relates to inducers utilized in liquid pumps. Specifically, the invention deals with axial flow inducers for imparting initial velocity to a liquid during a pumping procedure.

Difiiculty has been encountered in fluid pumps of the prior art in achieving eificient and high suction performance. Thisproblem has become particularly critical in the development of liquid propellant rocket engine systems. In such systems, large volumes of propellant must be pumped to the powerplant at high velocity and under a low net positive suction head (NPSH), i.e., the absolute total pressure of a liquid at the pump inlet center line less the vapor pressure of the liquid. Secondary flow Within the inducer flow channels and the existence of improper hydrodynamic loading of these channels have been primary contributing factors in such difiiculties. In this regard the flow channels are the channels defined between the inducer blades and secondary flow is intended to mean that flow within the channels which imparts no useful energy to the fluid. For example, flow from the blade tip to the blade hub and flow in a direction from the channel outlet toward the channel inlet may be termed secondary flow. These factors have also contributed to generally low suction specific speeds of such inducers, a result directly contrary to that desirable of achievement. Suction specific speed is a function of inducer rotational speed, fluid output and NPSH.

It is a primary object of this invention to provide an inducer capable of high suction performance.

Another object is to provide an inducer with materially reduced secondary flow.

A further object is to provide an inducer wherein only the leading edges of the blades thereof are hydrodynamically loaded.

A still further object is to increase pump suction specific speed.

Another object is to increase inducer channel area ratio.

Another object is to decrease net positive suction head required for pump operation.

Yet another object is to generally increase inducer efiiciency in imparting velocity to fluid to be pumped.

Other objects will become apparent from the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a diagrammatic representation illustrating blade lead;

FIG. 2 is a semi-schematic drawing of an inducer hub with a single blade thereon to illustrate blade cant angle;

FIG. 3 is a schematic representation of the inducer in plan view;

FIG. 4 is an elevation in partial section illustrating the inducer of the invention typically installed as a portion of a centrifugal pump; and

FIG. 5 is a front view of the inducer installed within its housing as taken essentially along lines 5-5 of FIG. 4.

The inducer of this invention is generally comprised of a rotatably mounted blade support means constructed to 3,l6 3,l l Patented Dec. 29, l64

continuously decrease inducer fluid channel areas, and blade means supported on said support means in an approximately normal relation to an outer support peripheiy, the blade means-to-support means structural orientations being changed continuously between the fluid inlet and fluid outlet so as to increase suction performance and to improve hydro-dynamic loading and secondary flow characteristics.

More specifically, the blade support means is a tapered hub mounted upon a drive shaft for rotation therewith. At least one helical blade extends approximately normally from the hub surface. Blade lead and blade angle change continuously from the fluid inlet to the fluid outlet, as does the difference between the blade lead at the hub attachment and at the blade tip.

As used herein, blade lead means the axial distance over which the blade is disposed as viewed in one complete revolution of the blade on the hub. Blade lead of the present inducer is diagrammatically illustrated in FIG. 1 as a trace of the axial distance (usually measured in inches) encompassed by an inducer blade in a complete revolution about the hub. The lead increases continuously from inducer inlet to outlet, resulting in a dimension at x greater than at y.

Blade cant angle is the angle defined between a line perpendicular to the hub axis and the blade center line. This angle, alpha (a), is semi-schematically illustrated in FIG. 2.

Blade angle is defined as the angle measured between a line normal to the hub axis and a tangent to the center line of the helical blade. Such blade angle is representatively illustrated in the semi-schematic inducer illustration of FIG. 3 wherein the inducer hub is indicated by dotted lines 19 and the blades by numeral 11. The inducer hub axis is indicated as 12, a perpendicular to the hub axis as 13 and the tangent to the blade center line is indicated by numeral 14. The blade angle, beta (#2), is the angle defined between lines 13 and 14.

Angle of attack is the difference beween relative fluid angle at the inducer inlet and the blade angle, the relative fluid angle, i.e., the angular resultant between the path of the blades leading edge and the absolute direction of the fluid into the inducer, being approximated by arrow 15 of FIG. 3. Arrow 16 indicates the absolute direction of fluid fiow in its approach to the inducer.

Referring now to FIG. 4, the inducer of this invention, generally indicated therein as 24), is mounted upon and for rotation with a shaft 21. It is secured against relative axial movement by retaining cap 22 and shoulder 21a and against relative rotation by key means 23 or other conventional means. Shaft 21 is usually integral with or otherwise attached to and adapted to rotate with a second shaft portion 24. The present inducer, as typically applied, is adapted to function with an impeller, indicated as 2.5 in the FIG. 4 embodiment. Impeller 25 is mounted for rotation with or about shaft portion 2%. Inducer 2t} and its associated structure are mounted within a housing 26 which contains a fluid passage 27, inducer Ztl being concentrically disposed within passage 27.

The inducer includes a hub 39 having an external surface 31 which tapers outwardly or divergently from the inducer inlet to the outlet. Hub surface 31 may be tapered at an angle of from about 8 to about 16 with respect to the hub axis. A preferred range of taper is from about 10 to 14 and a 12 angle is specifically preferred. .Alternatively stated, the hub is substantially conical, the diameter of the rearward hub extremity being preferably about twice that of the forward extremity. When fluid passage 27 is substantially cylindrical, this hub tapering serves to continuously decrease fluid channels 32 which are defined between blades 33 (described below), housing 26 and hub surface 31 in a substantially linear manner as the exit or outlet region is approached. The resultant change in area ratio (area at inlet divided by area at outlet) of the fluid channels enhances inducer performance over standard inducers by essentially matching the decrease in channel area to the increase in fluid velocity. In a typical application of the present inducer the area ratio is from 1.65 to 1.25, preferably 1.15.

Integrally extending from hub surface 31 and having its center lines at approximately right angles thereto is at least one inducer blade 33. In the preferred embodiment three such inducer blades are provided. It will be noted that so long as the substantially perpendicular blade-to-hub relationship is maintained the blade cant angle referred to above will be determined by the taper of hub surface 31. For example, if the hub taper is to be 12 the blade cant angle will likewise be 12. This forward canting of the blades provides a greater energy addition to the fluid at the outer blade peripheries than do conventionally oriented blades. This has the beneficial effect of reducing secondary flows which normally tend to reduce suction performance.

The leading edges 34 of blades 33, beginning at the forward hub extremity, are swept back and blended substantially as illustrated in FIG. 5. They are also carefully sharpened to essentially identical shapes. These features contribute to efficient performance.

When inducer 20 is rotated the blade outer peripheries 3 5 generates a substantially cylindrical pattern. The housing cavity within which the inducer is disposed matches this pattern with only a sufficient clearance to facilitate inducer rotation without metal-to-metal contact.

The inducer blade angle (defined above) increases continuously and non-linearly between the inducer inlet and outlet, the lowest practicable angle being from approximately 11 at root mean square (R.M.S.) diameter at the inlet to approximately 14 at the outlet. In the usual case, the increase is approximately 36 minutes. For example, the blade angle of one successfully operating inducer continuously increases from 12 (,6) at R.M.S. at inlet to 1236 3) at R.M.S. at outlet. An even superior blade angle varied from 13 at inlet to 1336 at outlet. The incorporation of this varying feature results in hydro-dynamically loading only the leading edge of the blades, a highly desirable result.

Blade lead is interrelated to the change in blade angle and inducer size. It also changes continuously from inlet to outlet and contributes materially to the success of the present inducer.

As an example of blade lead in a typical application, a blade lead of about 2.6 inches per revolution at the inlet and changing to about 2.9 inches per revolution at the outlet on an inducer having an axial length of approximately 2% inches, a blade tip diameter of approximately 5 inches and a hub increasing in diarneter from 1 inch to 2 inches has been found effective in producing superior inducer performance. A preferred change in blade lead from inlet to outlet on an inducer of the noted dimensions is from approximately 2.6 inches to approximately 2.9 inches. Ideally, the change in lead in the inducer of this invention matches the change in the velocity of the liquid as the outlet is approached. This prevents hydrodynamic loading in the fluid channel by compensating for the reduced channel area due to hub taper.

An inducer blade angle of attack of about 5 to 6 at R.M.S. results in near optimum performance. A blade angle of approximately 13 at R.M.S. assists in approaching this angle of attack optimization, thereby further contributing to improved performance.

Blades 33 are tapered from their points of attachmeat at hub 38 to their tips 35, the amount of taper or blade thickness at any designated point along its axis being dependent upon the load which the blades must be capable of accepting. The blades should be as thin as possible consistent with structural integrity.

Operationally, fiuid to be ultimately pumped radially outward by impeller 25 has an initial velocity imparted to it by inducer it? prior to its entrance into the impeller region. The fiuid to be pumped enters fiuicl passage 27 in the general direction indicated by the inlet arrow in FIG. 4. The fluid is intercepted by blade leading edges 34 in a manner whereby the leading edges are hydrodynamically loaded and a driving force is imparted to the fiuid by rearward surfaces 37 of blades 33, the force acting to increase the fluid velocity as the inducer outlet is approached. The fluid velocity increases continuously while the fluid is contained within fluid channels 32. This results from the net effect of the continuously changing lade lead and blade angle, and the hub taper in providing a continuously changing fiuid channel area.

Through the utilization of the described inducer where in secondary iiows of the pumped fluids are reduced or obviated, channel hydrodynamic loading is prevented to a substantial degree, superior suction performance is ac complished. inducer suction specific speed is greatly increased, and turbo-machinery to which the inducer is adapted is capable of operation with materially reduced net positive suction head. This has resulted in simplification of pumping systems. Since reduced pressurization of stored propellant is thus possible in the case of pumping from rocket propellant tanks the weight of the tanks is also capable of reduction in a significant amount.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of tlis invention being limited only by the terms of the appended claims.

We claim:

1. An inducer comprising a blade support means having a peripheral surface and mountable upon a drive shaft for rotation therewith, means forming a housing fluid passage concentrically and substantially coextensively surrounding said blade support means, said support means constructed to continuously decrease the fluid passage area from an inlet region to an outlet region thereof, blade means fixed to said support means and disposed helically about same in a substantially normal relation to said peripheral surface and canted forwardly of the drive shaft axis and with a continuously increasing blade angle and blade lead whereby inducer performance is enhanced.

2. The inducer of claim l wherein an external extremity of said blade means generates a substantially longitudinally extending cylindrical pattern when said inducer is rotated about its axis through at least one complete revolution.

3. The inducer of claim 1 wherein said blade support means comprises a hub having an external surface tapered outward from a first to a second end thereof, the ratio of the diameters of said ends being approximately 1:2.

4. An inducer comprising a rotatably mountable hub having a peripheral surface substantially conically tapered outward between first and second ends thereof, a helical blade extending from said hub approximately perpendicular to said surface and canted forwardly of the hub axis, said blade disposed at a blade angle continuously increasing from said first end to said second end.

5. The inducer of claim 4 wherein said blade angle increases approximately one half degree between said first end and said second end.

6. The inducer of claim 4 wherein said blade has a lead changing continuously from said first end to said second end.

7. The inducer of claim 4 wherein said blade has a lead change substantially proportional to a change in the velocity of liquid traversing said inducer when said inducer is rotated in a fluid stream.

8. An inducer mountable for rotation about a central axis thereof and comprising a hub having first and second ends, and a peripheral surface substantially conically tapered between side ends, a helically extending blade upstanding from said surface approximately normal thereto and canted forwardly of said central axis, the angle defined between a line normal to the hub axis and a tangent to the centerline of the helicalblade increasing continuously from said first end to said second end, the outer extremity of said blade so'terminating as to generate a substantially cylindrical pattern when said inducer is rotated about its axis, said blade having a lead increas ing continuously from said first end to said second end.

References Cited in the file of this patent UNITED STATES PATENTS 907,591 Gilday Dec. 22, 1908 1,887,417 Mawson Nov. 8, 1932 2,159,278 Lesley May 23, 1939 2,846,952 Ridland Aug. 12, 1958 2,920,347 Joukainen et al. Jan. 12, 1960 2,956,502 Glaser et al. Oct. 18, 1960 2,968,249 Caine et al. Jan. 17, 1961 3,068,799 Lock Dec. 18, 1962 FOREIGN PATENTS 783,468 Great Britain Sept. 25, 1957 

1. AN INDUCER COMPRISING A BLADE SUPPORT MEANS HAVING A PERIPHERAL SURFACE AND MOUNTABLE UPON A DRIVE SHAFT FOR ROTATION THEREWITH, MEANS FORMING A HOUSING FLUID PASSAGE CONCENTRICALLY AND SUBSTANTIALLY COEXTENSIVELY SURROUNDING SAID BLADE SUPPORT MEANS, SAID SUPPORT MEANS CONSTRUCTED TO CONTINUOUSLY DECREASE THE FLUID PASSAGE AREA FROM AN INLET REGION TO AN OUTLET REGION THEREOF, BLADE MEANS FIXED TO SAID SUPPORT MEANS AND DISPOSED HELICALLY ABOUT SAME IN A SUBSTANTIALLY NORMAL RELATION TO SAID PERIPHERAL SURFACE AND CANTED FORWARDLY OF THE DRIVE SHAFT AXIS AND WITH A CONTINUOUSLY INCREASING BLADE ANGLE AND BLADE LEAD WHEREBY INDUCER PERFORMANCE IS ENHANCED. 